Observation of Exciton–Exciton Interaction Mediated Valley Depolarization in Monolayer MoSe
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Author(s)
Mahmood, Fahad
Alpichshev, Zhanybek
Lee, Yi-Hsien
Kong, Jing
Gedik, Nuh
Date Issued
December 2017
Journal
Nano Letters
Publisher
American Chemical Society (ACS)
Citation
Mahmood, Fahad et al. “Observation of Exciton–Exciton Interaction Mediated Valley Depolarization in Monolayer MoSe2.” Nano Letters 18, 1 (December 2017): 223–228 © 2017 American Chemical Society
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Author's final manuscript
Abstract
The valley pseudospin in monolayer transition metal dichalcogenides (TMDs) has been proposed as a new way to manipulate information in various optoelectronic devices. This relies on a large valley polarization that remains stable over long time scales (hundreds of nanoseconds). However, time-resolved measurements report valley lifetimes of only a few picoseconds. This has been attributed to mechanisms such as phonon-mediated intervalley scattering and a precession of the valley pseudospin through electron-hole exchange. Here we use transient spin grating to directly measure the valley depolarization lifetime in monolayer MoSe₂. We find a fast valley decay rate that scales linearly with the excitation density at different temperatures. This establishes the presence of strong exciton-exciton Coulomb exchange interactions enhancing the valley depolarization. Our work highlights the microscopic processes inhibiting the efficient use of the exciton valley pseudospin in monolayer TMDs. Keywords: Transition metal dichalcogenides; valley polarization; 2D materials; valley dynamics; exciton interactions
MIT Department
Massachusetts Institute of Technology. Department of Physics
Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science
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Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.
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DOI of Published Version
https://doi.org/10.1021/ACS.NANOLETT.7B03953
